Gas Metal Arc Welding (GMAW) is an arc welding process in which an electrical arc is established between a continuously fed consumable electrode and the base metal to be welded. In GMAW, energy from the arc is used to melt the base metal and the electrode. Droplets form on the tip of the molten electrode and are transferred across the arc. An inert or slightly reactive shielding gas is provided in the arc region to reduce the reaction of the base metal, molten electrode, and arc due to contamination by the atmosphere. A constant potential power source is used to hold the arc voltage constant for a given electrode feed rate via an internal feedback control. Disturbances in the arc region such as shielding gas contamination, weld pool interference, and excessive melt-through can be detected in the current and voltage signals as the power source compensates for these events.
Prior arc welding strategies have sensed variations in the current signal or voltage signal in order to track the weld seam, adjust the fill volume, or detect shielding gas contamination in pulse welding. For example, see U.S. Pat. No. 5,221,825 issued on Jun. 22, 1993 to Siewert et al. in which electrical signals are sampled to determine shielding gas quality, the occurrence of short circuits and frequency thereof, pulse frequency and standard deviation thereof, contact tube wear and trends in the sampled electrical signals.
Still, there is always a need for improved arc welding fault detection strategies. Preferably, such strategies should resolve the quality state of the weld based on the characteristics of the welding current and voltage signals. Also, such strategies should resolve one or more quality states of the weld using real time processing so that the weld operator can be immediately alerted to a poor weld and/or the weld process can be immediately terminated. Further, such strategies should be capable of being practically implemented at a speed sufficient to avoid producing defective welds due to the formation of porosity, excessive convexity, and/or excessive melt-through.